Highly deviated drilling programs and horizontal wells are becoming widely used to access reservoirs. Due to the steep angle of these deviated wells, high bending stresses are induced in drill pipes that rotate within curved portions of the well. With these high bending stresses, the drill pipe connections may develop fatigue cracks at their thread roots. These fatigue cracks can lead to washouts or even failure. It has previously been established in conventional “V” threads that increasing the root radius of the thread form aids in the reduction of the connections' peak stresses. Most drill pipe manufactures are now designing connections to help in the reduction on the connection fatigue stresses by applying this method.
In developing these new connections by the above mentioned method, designers have to compromise with the reduction in torque and or tensile capacity of the connection due to the geometry of the connection, which is highly affected by the thread form design. In some cases, designers will have to undercut the threads to produce a larger root radius. These undercuts may further reduce the performance of the connection in torque and tensile capacity.
Taking in mind the above current design status of the drill pipe connections in the existing market, there is a need to develop a change in geometry evolving from the conventional “V” threads to achieve not only a high level of fatigue resistance to bending stresses, but also to achieve higher torque and tensile requirements within the given design area. In addition, it is also desirable to develop a threaded connection that forms a slim hole profile design in order to minimize the pressure loss within the well and to aid in the removal of cuttings and debris from the well.